Mushaka (or Muushika, or Mooshika, etc.) is either a rat or a mouse or perhaps kind of both. This being a story from India and thereabouts it doesn't seem likely that Mushaka would be a Norway rat, in any event; but I think of him as one just the same. I have never met a black rat, Rattus rattus, such as they have so many of in that part of the world, so I don't know what their personalities are like. They have lots of them in the American South as well, though, so perhaps some of you know if it would be a good idea to trust one with unlimited power. In Texas I believe they are known as tree rats or roof rats.
A Norway rat would use unlimited power to obtain an unlimited supply of raisins and bacon and Nutella, and a big soft pile of friends to nap and play with.